1. Field of the Invention
The present invention relates to a scanning-type exposure apparatus for scanning a mask (or a reticle) and a substrate synchronously to transfer a pattern of the mask to the substrate in a photolithography process for manufacturing, e.g., a semiconductor, a liquid crystal display device or a thin film magnetic head and more particularly to an exposure apparatus of a step-and-scan system for transferring a pattern of a mask to each of a plurality of shot areas on a substrate successively on a scanning exposure system.
2. Related Background Art
In a photolithography process for manufacturing a semi-conductor or the like, a projection-type exposure apparatus is utilized in which the image of a pattern on a mask or a reticle (hereinafter referred to as the reticle) is transferred via a projection optical system to a photosensitive substrate (a wafer or glass plate with photoresist applied thereto). Recently, the sizes of semiconductors tend to be large and in projection-type exposure apparatuses, it is required to transfer a much larger pattern on a reticle to a photosensitive substrate.
Then, for example, scanning-type exposure apparatuses have been developed in which a reticle and a wafer are scanned synchronously with respect to a rectangular, circular arc or hexagonal illumination area (hereinafter referred to as the slit-like illumination area) to transfer a pattern larger than the slit-like illumination area to the wafer. Such apparatuses are disclosed in e.g. U.S. Pat. Nos. 4,747,678, 4,924,257, 5,194,893, 5,281,996, 5,227,839 and 5,255,051.
Particularly, in scanning and exposing a pattern on a reticle to each of a plurality of shot areas on a wafer, after an exposure for the first shot area has been completed, the stepping of the wafer is carried out so as to position the following shot area to a scanning start position. This system of repeating the stepping and the scanning exposure is called a step-and-scan system. The system of scanning the reticle and the wafer synchronously so as to transfer the pattern of the reticle to the wafer including the step-and-scan system is called xe2x80x9cthe scanning exposure systemxe2x80x9d hereinafter.
There are reticles in which each pattern area has a plurality of identical (or different) chip patterns. In this case, when carrying out scanning exposure by means of a stepper adopting a batch exposure processing system, the image of the whole patterns on such a reticle is projected even to each of shot areas located in the periphery of the wafer to which only a portion of the plurality of patterns can be projected (hereinafter referred to as the incomplete shot areas).
When transferring a plurality of chip patterns on a reticle to each of incomplete shot areas on a wafer on the scanning exposure system, the reticle and the wafer are scanned for length (the length of the full field) the same as when the whole chip patterns on the reticle are transferred to the wafer. Therefore, unnecessary portions of the incomplete shot areas (e.g., the peripheral end portion of the wafer) are exposed also. Therefore, time is wasted for scanning the unnecessary portions, which causes the exposure time per shot to become long. As a result, the throughput is lowered.
It is an object of the present invention to provided a scanning-type exposure apparatus in which when using a plurality of circuit patterns (chip patterns) arranged along a scanning direction or a non-scanning direction perpendicular to the scanning direction and exposing a plurality of shot areas on a photosensitive substrate on a step-and-scan system, the total time for moving the mask and/or performing the stepping of the substrate other than the time for exposing effective areas of the shot areas on the substrate is shortened to improve the throughput of the exposure process.
The present invention concerns on exposure method in which a mask stage for holding a mask and moving it in a first direction and a substrate stage for positioning a photosensitive substrate two-dimensionally and moving it in a direction corresponding to the first direction are used, and the pattern of the mask is transferred to each of a plurality of shot areas by positioning each of the shot areas to a scanning start position by a stepping operation of the substrate stage, and scanning the mask and the substrate synchronously by driving the mask stage and the substrate stage.
In the first method of the present invention, when exposing and scanning, with a mask having a plurality of circuit patterns arranged in a first direction, among a plurality of shot areas on a substrate, an incomplete shot area in the peripheral portion of the substrate to which one or several of the plurality of circuit patterns on the mask can be transferred, the mask and the incomplete shot area on the substrate are moved to respective scanning start positions by driving the mask stage and the substrate stage, and in synchronism with moving the mask by means of the mask stage along the first direction for a distance corresponding to the total width of the one or several of the plurality of circuit patterns to be transferred to the incomplete shot area, the substrate is moved by the substrate stage along a second direction for a distance corresponding to the total width of the image of the one or several of the plurality of circuit patterns to be transferred to the incomplete shot area. Also, after the scanning exposure, the mask stage is driven at a permissible highest speed to set the mask to the following scanning start position, and the substrate stage is driven to set a shot area on the substrate to be exposed next to a scanning start position.
It is preferable to provide, in an illumination optical system for emitting light to the mask, a variable field stop for varying the shape and/or the size of an illumination area on the mask. By changing the shape and/or the size of the illumination area by the use of the variable field stop during the scanning exposure, only the one or several of the plurality of circuit patterns to be transferred to the incomplete shot area is illuminated with light from the illumination optical system. That is, the circuit patterns other than the one or several circuit patterns are made not to enter the illumination area.
In the second method of the present invention, when scanning and exposing an incomplete shot area on a substrate with a mask having a plurality of identical circuit patterns along a second direction perpendicular to a first direction, the mask and the substrate are scanned synchronously by driving the mask stage and the substrate state after the incomplete shot area is overlapped with the image of the plurality of circuit patterns in the second direction for the total width of the image of the one or several of the plurality of circuit patterns on the mask, and the patterns other than the one or the several patterns are covered.
According to the first method of the present invention, for example, as shown in FIG. 2, the pattern area of a mask (R) is divided into, e.g., three sub-pattern areas (PA1 to PA3) along a first direction (scanning direction), and the same or different chip patterns are formed on the respective sub-pattern areas. As shown, for example, in FIG. 6, in a shot area (SA6) in the peripheral portion of a wafer (W), only one of the three chip patterns on the mask (R) can be transferred. Also, in an adjacent shot area (SA7) to be exposed next, only two chip patterns can be transferred. That is, those shot areas (SA6, SA7) are incomplete shot areas.
Only the chip pattern of one sub-pattern area (PA3) on the mask (R) is exposed to the incomplete shot area (SA6) on the substrate (W). Therefore, in FIG. 2, in synchronism with scanning the sub-pattern area (PA3) with respect to an illumination area (21), one-third of the shot area (SA6) on the substrate (W) is scanned with respect to an area corresponding to the illumination area (21) in a direction opposite to a locus (T6). Thereafter, the stepping of the substrate stage is performed at a permissible highest speed to set the shot area (SA7) on the substrate (W) to a scanning start position. In parallel to the stepping operation, the mask stage is driven at a permissible highest speed in a direction corresponding to a locus (U6) to set the second sub-pattern area (PA2) on the mask (R) to a scanning start position. Then, in synchronism with scanning only the sub-pattern areas (PA3, PA2) on the mask (R) with respect to the illumination area (21), two-thirds of the shot area (SA7) is scanned in a direction opposite to a locus (T7). Owing to such a sequence, the time for moving the mask and performing the stepping of the substrate other than the time for exposing the effective areas (here, the one-third, or two-thirds of the shot area) of the shot areas on the substrate (W) is shortened.
In the scanning exposure system, a predetermined approach run period (distance) is required until the mask (R) and the substrate (W) are scanned at respective constant speeds. In order to prevent the pattern of the mask (R) from being transferred to the substrate (W) during the approach run period, it is necessary to perform an operation for stopping the light emission of a light source for exposure, shielding light from the light source by means of a shutter, or closing the illumination area (21) by making the width of the illumination area (21) variable. In order to make the width of the illumination area (21) variable, it is preferable as shown in FIG. 1, to provide a variable field stop (6A, 6B, 7) in a plane conjugate to the pattern surface of the mask or in the vicinity of the plane. For example, when transferring only the chip patterns of two sub-pattern areas (PA1, PA2) of the mask (R) in FIG. 2 to the substrate (W), the sub-pattern area (PA3) is prevented from entering the illumination area (21) by means of the variable field stop, as shown in FIGS. 4A to 4C.
Also, in the case of making the width of the illumination area (21) variable by means of the variable field stop, for example, in FIG. 6, when the stepping of the substrate (W) is performed from the shot area (SA6) to which only the chip pattern of one sub-pattern area can be transferred to the shot area (SA7) to which the chip patterns of two sub-pattern areas can be transferred, the mask (R) is scanned for an amount corresponding to the amount indicated by the locus (U6) on the shot area (SA6) in the state with the illumination area closed. Then, in the following shot area (SA7), in synchronism with scanning the mask (R) in the direction opposite to the scanning direction of the mask in the shot areas (SA6) for an amount corresponding to the locus (T7) in the state with the illumination area (21) opened, the substrate (W) is scanned in the direction opposite to the locus (T7). Thereby, unnecessary movement of the mask is prevented, making it possible to shorten the exposure time.
In short, it is desirable to set an exposure sequence in accordance with the following rules in order to shorten the exposure time.
(1) In the complete shot areas on the substrate (W), exposure is not performed to a portion to which the pattern of one or two sub-pattern areas among the plurality of sub-pattern areas (PA1 to PA3) cannot be exposed completely.
(2) In the shot areas (SA1 to SA68) on the substrate (W), the patterns of the sub pattern areas (PA1 to PA3) are transferred to corresponding effective portions.
(3) When scanning and exposing the plurality of shot areas successively, the scanning directions of the shot areas are changed alternately oppositely. Thereby, the mask (R) repeats a simple reciprocating motion.
(4) After one shot area on the substrate (W) has been exposed, in parallel with performing the stepping of the substrate (W) by means of the substrate stage (14) to set the following shot area to a scanning start position, the mask (R) is moved to a scanning start position.
According to the second method of the present invention, for example, as shown in FIG. 9, a plurality of identical circuit patterns (PA4, PA5) are formed on a mask (R) along a second direction (non-scanning direction) perpendicular to a scanning direction and only one circuit pattern (PA5) on the mask (R) can be transferred to a shot area (SH1) on a substrate (W) in FIG. 10. Further, the width of the shot area (SH1) in the non-scanning direction is H and the width thereof in the scanning direction is V. When scanning and exposing the shot area (SH1), the shot area (SH1) is overlapped with the projected image (30A) of the plurality of circuit patterns on the mask in the non-scanning direction for the width H/2, and only the circuit pattern (PA5) on the mask (R) is scanned with an illumination area (21A), as shown in FIG. 9. Thereby, the circuit pattern is transferred to only the overlapped portion (effective portion) within the shot area (SH1). Next, when scanning and exposing a shot area (SH2) adjacent to the shot area (SH1) in the non-scanning direction, the stepping of the substrate (W) is performed for H/2. Therefore, the amount of stepping is half of the amount of stepping according to the conventional exposure method, whereby the throughput of the exposure process is improved.